Our main research interests reside in the intracellular events -changes in signaling and in gene expression- which direct T-lymphocyte differentiation and survival, both during intrathymic T-cell development and in mature T-cells. Our first experimental approach focuses on T-cell positive selection, an intrathymic process induced by T-cell Receptor (TCR) engagement and which ensures the generation of an efficient T-cell repertoire by rescuing 'useful' thymocytes from programmed cell death and by inducing their differentiation into mature T-cells. Our objective here is to identify the changes in gene expression responsible for these events, not only by comparing gene expression patterns between pre-selection and mature T-cells, but also by identifying transient changes in gene expression that are critical to the process. To this end, we generated a recombinant mouse model in which Zap70, a protein tyrosine kinase required for TCR signal transduction, becomes insufficient as the cell moves along the positive selection process. Consequently, while normal numbers of thymocytes appear to initiate positive selection, they fail to survive and to complete their maturation program. We now want to use this model to examine which part of the differentiation/survival program the mutant thymocytes fail to initiate, (i) by comparing gene expression patterns in the arrested thymocytes to those in preselection and mature thymocytes and (ii) by identifying genetic alterations which complement the late defect in TCR signaling. We are also developping conditional versions of intracellular signaling molecules that can be turned 'on' or 'off' by small-size ligands, to interfere with T-cell signal transduction in vivo and to monitor signaling and gene expression during the course of an immune response or during intrathymic development of T-cell precursors. The project started in the LICB on February 28, 2000.